. The nephric duct is a central component of the vertebrate excretory system. During development of the vertebrate urogenital system, the product of the c-ret proto-oncogene is expressed on the migrating tip of the nephric duct primordium and its epithelial derivatives, but not the surrounding nephric mesenchyme. When Ret kinase activity is eliminated from these tissues via germline transformation in mice, the neonates die as a result of severe renal dysgenesis. These data establish the requirement for c-ret in development of the urogenital system, but fail to reveal which nephric duct function is affected by loss of Ret kinase activity. The prinicpal investigator proposes to investigate the function of c-ret in posterior extension, differentiation, and inductive properties of the nephric duct. These experiments will be performed on axolotl embryos. In the experiments proposed, the investigator will clone and sequence c-ret from axolotl tailbud stage cDNA library. She will then determine the spatio-temporal expression of c-ret by Northern blot and in-situ hybridization during stages 15-30 of axolotl development. Functional analysis of the Ret protein will be accomplished by raising antibodies to extracellular domains of axolotl Ret then performing in vivo chromophore-assisted laser inactivation (CALI) to eliminate Ret from the nephric duct primordium. The functional studies are designed to allow spatial and temporal control over Ret protein inactivation. This work should allow the investigator to determine the developmental time within which c-ret function is required. Since axolotl nephric duct morphogenesis is easily observed and manipulated the investigator should be able to determine whether growth, differentiation, migration and/or inductive functions of the nephric duct are perturbed in the absence of Ret.